The code pane shows a couple of warning messages. One in particular is a BIG hint…
You already have completePrice declared as a global variable. By declaring it as a local in the onItemReady() function means that the values aren’t added.
Delete the let so your line of code looks like this:
completePrice = completePrice + getPrice(iD) * quantity;
I would also recommend changing the variable iD (indicated in the screen shot) to something unique just to avoid possible conflicts.
I hope this helps,
Yisrael